1. Field of the Invention
The present invention relates to a process for manufacturing tyres for vehicle wheels.
The invention further relates to an apparatus for the deposition of an annular reinforcing structure in the building step of a carcass structure of a tyre for vehicle wheels, said apparatus being usable in carrying out the aforementioned process.
2. Description of the Related Art
A tyre for vehicle wheel generally comprises a carcass structure comprising at least one carcass ply comprised of reinforcing cords incorporated in an elastomeric matrix. The carcass ply has end edges respectively engaged with annular anchoring structures arranged in the zones usually identified with the name of “beads” and normally consisting each of a substantially circumferential annular insert on which at least one filling insert is applied, in a radially outer position thereof. Such annular structures are commonly identified as “bead cores” and have the task of keeping the tyre well fixed to the anchoring seat specifically provided in the rim of the wheel, thus preventing, in operation, the radially inner end edge of the tyre coming out from such seat.
At the beads specific reinforcing structures may be provided having the function of improving the torque transmission to the tyre. The region of the bead, indeed, is particularly active in the torque transmission from the rim to the tyre in acceleration and braking, and therefore the provision of appropriate reinforcing structures in such an area ensures that the torque transmission occurs with the maximum possible reactivity.
In a radially outer position with respect to the carcass ply, a belt structure comprising one or more belt layers is associated, said belt layers being arranged radially one on top of the other and having textile or metal reinforcing cords with crossed orientation and/or an orientation substantially parallel to the direction of circumferential extension of the tyre.
Between the carcass structure and the belt structure a layer of elastomeric material, known as “under-belt”, can be provided, said layer having the function of making the radially outer surface of the carcass structure as uniform as possible for the subsequent application of the belt structure.
In a radially outer position with respect to the belt structure a tread band is applied, also made from elastomeric material, as well as other structural elements making up the tyre.
Between the tread band and the belt structure a so-called “under-layer” of elastomeric material can be arranged, said layer having properties suitable to ensure a steady union of the tread band itself.
On the side surfaces of the carcass structure respective sidewalls of elastomeric material are also applied, each extending from one of the side edges of the tread band up to the respective annular anchoring structure to the beads.
Throughout the present description and in the following claims, the term “reinforcing element” is used to indicate a cut to size element comprising one or more thread-like reinforcing elements substantially parallel to one another, such as textile or metal cords, embedded in, or coated with, a layer of elastomeric material.
The term: “elastomeric material” on the other hand is used to indicate a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such a composition further comprises additives such as, for example, a cross-linking agent and/or a plasticizer. Thanks to the provision of the cross-linking agent, such material can be cross-linked by heating, so as to make the end product.
The traditional processes for manufacturing tyres for vehicle wheels essentially provide for the components of the tyre listed above to be first made separately from one another, to be then assembled in a subsequent building step of the tyre.
However, the current tendency is that of using manufacturing processes that allow the production and storage of semi-finished parts to be minimised or possibly eliminated. In such processes, each component of the tyre is directly formed on a forming support, for example as illustrated in EP 0 928 680 in the name of the same Applicant.
More specifically, attention has now turned towards process solutions that allow the individual components of the tyre to be made by directly applying them, according to a predetermined sequence, onto the tyre being built on a forming support, typically toroidal or cylindrical.
JP 2006-205769 describes a process for manufacturing a reinforcing structure of the bead region of the tyre, wherein such a reinforcing structure is obtained in the form of a strip by reciprocally joining a plurality of reinforcing elements obtained cutting to size band-like pieces of a continuous band-like element which incorporates metal reinforcing elements. According to an embodiment described in the aforementioned document, a sheet of elastomeric material is made by arranging a plurality of cords in the same direction and coating them with elastomeric material. Said sheet is then repeatedly cut along the direction of the cords to obtain band-like pieces having a parallelogram shape. A ring-shaped sheet of reinforcing material is then formed by sequentially attaching each band-like piece along a circumference defined on a side surface of a tyre being formed in toroidal configuration, the band-like piece being deformed in such a way that the length of an outer peripheral portion of the sheet of reinforcing material forms a curve arc longer than the length of the inner peripheral portion of the sheet of reinforcing material. The same document illustrates an embodiment wherein each band-like piece is attached, without being deformed, to a portion defined on the same circumference corresponding to the portion of the bead of the tyre being formed in toroidal configuration.
Patent application published as WO 2007/138374, in the name of the same Applicant, describes a process for manufacturing a tyre for vehicle wheels wherein the reinforcing structure is formed by depositing a plurality of reinforcing elements along a curvilinear deposition path defined at each end edge of a carcass ply laying on a toroidal support. The reinforcing elements are obtained cutting to size band-like pieces of a continuous reinforced element and deforming these band-like pieces according to the bending of the portion of the deposition path where they will actually be deposited.
U.S. Pat. No. 6,379,493 describes an apparatus for carrying reinforcing elements previously cut from a continuous band-like reinforced element and depositing them on a forming support. The apparatus comprises two opposite arms, each provided, at the respective free end thereof, with a plurality of needles adapted to penetrate the reinforcing element for moving it up to the forming support, where it is then deposited. The needles are movable along respective longitudinal directions for allowing the pick up and the release of the reinforcing elements. The arms are mounted on a crosspiece sliding towards and away from the forming support along a direction tangential to the forming support. Such arms are rotatable around respective rotation axes so as to be lifted during the movement of the crosspiece away from the forming support and so as to be lowered again for picking up the reinforcing element and moving it towards the forming support for the subsequent deposition.
The Applicant has noted that in the processes described in the aforementioned patent applications WO 2007/138374 and JP 2006-205769, deposition of the reinforcing elements occurs first at an end edge of the carcass ply and, only after the reinforcing structure at such end edge has been completed, deposition of the reinforcing elements begins at the other end edge, so as to form a reinforcing structure also at this other end edge. In the process described in U.S. Pat. No. 6,379,493, on the other hand, deposition of the reinforcing elements is carried out simultaneously on opposite end edges of the carcass ply, working in parallel through two separate pivoted arms.